642 R. C. PUNNETT. 
but no giant cells are present such as have been figured by Spengel for B. apertus 
(?98, Taf. 7, fig. 18). Except at its anterior end the collar cord is sunk in the perihaemal 
spaces which embrace it on either side and which may posteriorly reach nearer to the dorsal 
surface than the cord itself. The medullary canal communicates with the exterior by the 
anterior and posterior neuropores. 
The first two dorsal roots are large, close together, and contain nerve fibrils but are 
devoid of a lumen. They spring from a common crest and reach the epidermis where their 
nerve fibrils fuse with the nervous layer of the skin. Behind these are two or three small 
incomplete roots with traces of a lumen but without nerve fibrils. 
A well-marked peripharyngeal space surrounds the cesophagus (Pl. XXXIX. fig. 24, pph.) 
reaching dorsally to where the cornua of the nuchal skeleton diverge, and ventrally somewhat 
anterior to this point. 
Branchial region. This region is characterized by the small genital pleurae which 
are widely separate at their junction with the collar. At the base of the pleurae open 
the gill pouches (Pl. XLI. fig. 1, bp.) which are not provided with ventral caeca. The branchial 
and digestive portions of the cesophagus are approximately of equal size. Gonads are not 
found in the anterior fourth of the branchial region. Not more than six synapticula are 
present on either side of the tongue bars. The post branchial canal is-large and the posterior 
incipient gill slits open into its ventral portion (Pl. XLI. fig. 2, *), 
Genital region. The great bulk of this region is occupied by the gonads in the 
much swollen pleurae (Pl. XLI. fig. 4). Accessory gonads are not present, but each gonad is 
roughly two-branched, one division lying on either side of the lateral septum. The genital 
pores are found on the edges of the pleurae at the spot where the lateral septum joins 
the epidermis. The single specimen was an adult female. 
Affinities. The genital pleurae of B. parvulus are relatively smaller than in any other 
member of the genus and in this respect it approximates to the genus Glossobalanus. Of 
the members of its own genus it bears most resemblance to B. apertus (Spengel, 798). 
In both the genital pleurae are widely separate where they join the collar, and this character 
serves to distinguish these two species from all the other members of the genus except 
B. misakiensis (Kuwano, ’02). Both B. parvulus and B. apertus are small forms without 
accessory gonads, with a tubular collar cord, and with gill pouches unprovided with a ventral 
caecum. The present species however differs from B. apertus in the following features. 

B. parvulus | B. apertus 
Branchial region but little longer than the collar. Branchial region several times as long as collar. 
Gonads open at edges of genital pleurae. Gonads open on inner surface of genital pleurae. 
No circular muscles to body-wall. Feeble circular musculature. 
Tongue bars with not more than 6 synapticula. | Tongue bars with about 10 synapticula. 
Medullary tube open at either end. Medullary tube closed at either end. 
Giant ganglion cells not found in collar cord. Giant ganglion cells present in collar cord. 
In B. parvulus also the keel of the nuchal skeleton is more marked, whilst the ventral 
proboscis coelom has undergone greater reduction. An idea of the relations of these two 
species with the other members of the genus may be gathered from the appended table. 
